Under barbiturate anesthesia 8-10/sec continuous slow wave activity occurs in the subthalamic nucleus and mesencephalic ventral tegmental area (VTA). Activity in the subthalamic nucleus leads that in VTA by 14 msec, which is the latency of the response evoked in VTA by subthalamic stimulation. Lesions in the subthalamic nucleus, or along a pathway coursing through nucleus ventralis anterior, lateral habenular region and along the habenular region and along the habenulo-interpeduncular tract, abolish the rhythmic activity in VTA. Globus pallidus or entopeduncular nucleus stimulation inhibits the slow wave activity for 300-500 milliseconds. This study will (a) examine the relationship between the rhythmic slow wave activity and unit discharge in VTA and subthalamic nucleus, (b) seek the location of the "pacemaker" neurons responsible for this rhythmical activity and (c) study the site and mechanisms of the inhibition due to pallidal stimulation.